This invention relates in general to electrophotography and, in particular, to electrophotographic imaging members and processes for preparing the imaging members.
In electrophotography, an electrophotographic plate containing a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging its surface. The plate is then exposed to a pattern of activating electromagnetic radiation, such as light. The light selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated area. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the electrophotographic plate to a support such as paper. This imaging process may be repeated many times with reusable photoconductive insulating layers.
An electrophotographic imaging member may be provided in a number of forms. For example, the imaging member may be a homogeneous layer of a single material or may be a composite containing a photoconductor and another material.
One type of multilayered photoreceptor which has been employed as a belt in electrophotographic imaging systems is described in U.S. Pat. No. 4,786,570 to Yu et al. This electrophotographic imaging system comprises a substrate, a conductive layer, a hole blocking layer, an adhesive layer, a charge generating layer, and a charge transport layer. This photoreceptor may also comprise additional layers such as an anti-curl back coating and an overcoating layer. In this imaging member, the hole blocking layer may comprise a reaction product between a hydrolyzed silane and an oxidized surface of a metal ground plane layer.
In fabricating electrophotographic imaging members, there is a need for materials which can be easily prepared and which have greater mechanical stability. There are known a number of methods and materials for forming electrophotographic imaging members.
The sol-gel process allows the preparation of a variety of inorganic ceramic glasses at low temperatures. Generally, a sol is formed from a suspension of liquid chemicals in a solvent. The sol is then polymerized and crosslinked through condensation to form a gel. A crosslinked glassy network is ultimately obtained by drying the gel to remove solvent trapped in the condensed product.
The concept of the sol-gel process is known and has been employed in various fields. For example, Yoldas et al in U.S. Pat. Nos. 4,753,827 and 4,754,012 disclose organoalkoxysilane/metal oxide sol-gel compositions which are abrasion-resistant, and a method for their production. An organoalkoxysilane or mixture of organoalkoxysilanes is mixed with a metal alkoxide or mixture of metal alkoxides. The mixture is hydrolyzed, condensed and dried to form an organosiloxane/metal oxide abrasionresistant coating.
Roy et al, "Multi-phase Ceramic Composites Made by SolGel Technique," Mat. Res. Soc. Symp. Proc., vol. 326, 1984, discloses the formation of photoconductive foams or species such as ZnO and CdS dispersed in inorganic gels.
Thin films of hybrid material composed of a silica network and polysiloxane flexible subunits have been disclosed by G. L. Wilkes et al, "Ceramics: Hybrid Materials Incorporating Polymeric/Oligomeric Species Into Inorganic Glass Utilizing a Sol-Gel Approach," Polymer. Prep., vol. 26, No. 3, page 300, 1985. The hybrid material was prepared by the hydrolysis and condensation of tetraethylorthosilicate (TEOS) to produce hydroxy terminated silicate, which is reacted with hydroxy terminated polydimethylsiloxane.
Although excellent toner images may be obtained with multilayered belt photoreceptors, it has been found that numerous layers limit the versatility of the multilayered belt photoreceptor. For example, there is a great need for flexible, long service life belt photoreceptors in compact imaging machines that employ small diameter support rollers due to the very confined space. Small diameter support rollers also allow for reliable copy paper stripping using the beam strength of the copy paper to remove it from the surface of a photoreceptor belt after toner image transfer. These small diameter rollers raise the threshold of mechanical performance criteria to such a high level that spontaneous photoreceptor belt material failure becomes a frequent event. Cracking may be encountered in one or more of the photoreceptor layers during belt cycling over small diameter rollers.
Moreover, multilayered belt photoreceptors tend to delaminate during extended cycling over small diameter support rollers. Alteration of materials in the various belt layers such as the conductive layer, hole blocking layer, adhesive layer, charge generating layer, and/or the charge transport layer to reduce delamination is not easily effected because the new materials may adversely affect the overall electrical, mechanical and other properties of the belt such as residual voltage, background, dark decay, flexibility and the like.
In multilayered photoreceptors, it is desirable not only to maintain the electrical and mechanical integrity of the device, but also to provide simple fabrication processes.